1. Technical Field
The present invention relates to a piezoelectric resonator, a manufacturing method thereof and a lid for a piezoelectric resonator.
2. Related Art
A piezoelectric resonator element is typically fixed within a package and enclosed therein with a lid. JP-A-2005-191314 is an example of related art. The example disclosed a lid that has a window through which the inside of the package can be optically seen even after the package is sealed with the lid. According to the example, a windowpane is fixed such that a glass plate whose size is smaller than a diameter of an opening of a metal frame and whose thickness is larger than the metal frame is placed so as to cover the opening of the metal frame, the glass plate is softened by heat then pressed and spread, and a part of the glass which protrudes out from the metal frame is ground and removed. Where the windowpane is fixed this way, there is a possibility that the glass plate can be broken by grinding. In addition, according to the example, the inner faces of the metal frame is curved so that the stress is easily concentrated in a part of the glass plate when a force works in the thickness direction of the metal frame and the glass plate and a direction in which the glass contracts and stretches, increasing the possibility of the breakage of the glass. Moreover, the lid has to be made thin in order to decrease the height of the piezoelectric resonator, there is a higher possibility of the breakage of the glass.